Ken YapWith a continuity tester I mapped out the I/O space. Besides the address lines, these lines also participate: /M1, /IOR. The devices and the corresponding bits that activate them, from A4 down to A0 are:
74LS138 1 of 8 decoder: 00XXX
Z8440 SIO: 01XXX
Z8430 CTC: 10XXX
The 74LS138 seems to have something to do with the power drive transistors.
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